The possibility that changes in acetylcholine content following drug treatment might reveal indirect information concerning its turnover rate necessitated a detailed comparison between killing animals by decapitation or by microwave radiation. The results suggest that changes in the turnover rate of striatal acetylcholine elicited by drugs cannot be predicted by a decrease or an increase in striatal acetylcholine content measured in rats killed by decapitation. The acetylcholine content and turnover rate were determined in rats receiving haloperidol or clozapine. Both drugs reverse the decrease in striatal turnover rate caused by apomorphine. The turnover rate of striatal acetylcholine is increased by haloperidol but not by clozapine. This difference could explain its extra-pyramidal action while the anticholinergic action of clozapine could explain its lack of extrapyramidal side effects.